l886.] NEW-YORK MICROSCOPICAL SOCIETY. 11 



in all slides. Specimens from different trees show different de- 

 tails. Our specimens were collected in November and Decem- 

 ber to date, which must be considered. 



In all probability the full cycle of development of P. viridis 

 in its habitat, cannot be determined without observations ex- 

 tending through the different months of a year, at least. Mr. 

 Southwick reports some trees as covered quickly during storms, 

 after he had cleaned them. Whether his solutions failed to de- 

 stroy all the germs, or they were supplied from other sources, is 

 being investigated. November 23d a heavy N. E. storm began in 

 this vicinity, i -^^^ inches of water fell in 24 hours, about ^\j of 

 the usual yearly rain fall. On the 24th the rain-fall was ^^-^ of an 

 inch. On the 23d the mean temperature was 35°, max. 38°, 

 miles traveled by the wind, 324. The next day the mean tem- 

 perature was 38.3°, max. 39°, miles traveled by the wind, 379, 

 according to Dr. Draper's meteorological records in Central 

 Park. On some trees the P. viridis seemed to be brighter, more 

 on the north-west side, than before the storm; but no new patches 

 were found, therefore fresh isolated growths did not occur during 

 this storm, and trees which had been just cleaned were exempt, 

 and on the deciduous trees, the water coursing down the bark 

 had removed it, leaving either side green. 



In P. vulgaris and P. pluvialis, resting and motile forms are 

 shown, besides those of subdivision ; in P. viridis we looked 

 through a great number of specimens for the motile forms, and 

 only found them in specimens collected during the last two or 

 three days. I had examined many which were dry when frozen, 

 and found only a few, but on taking some from a brick which 

 was hygroscopic, the plant being wet when frozen, I found an 

 abundance of motile forms. 



The cellulose sac, which surrounds the protoplasm, was burst, 

 and the latter escaped, assuming an oblong or elliptical form, 

 but not with one end double pointed as figured in P. vulgaris 

 and P. pluvialis. The statement that these motile forms have 

 two long cilia, so far has not been verified by our investigations. 

 The chloro-plastids seen in the motile forms are round, some 

 having two, and others four or five, giving the appearance of nu- 

 clei. Freezing several times does not destroy the motile form, 

 the delicate sac being flexible and elastic. On the shady side of 



